Apparatus for prestressing rods in concrete

ABSTRACT

A hydraulic stressing press to be used for stressing at least one rod, wire or wire bundle which is prestressed in a concrete structure. The housing of the press is adapted to be supported against an abutment member and is provided with an anchoring device and a clamping device. The anchoring device and the stressing device itself are actuated by hydraulic pistons. An externally located anchoring ring cylinder unit is provided, and at least one part of this unit surrounds an internal clamping device and is connected to a anchoring element removably arranged between the clamping device and the clamping jaws.

United States Patent Odilo Paul [72] Inventor [56] References Cited Durmentinger/Wurtt., Germany P 827427 3,338,553 8/1967 Periske 254 29 [22] FM May 1969 3 491 431 1 1970 Pewitt 254/29 x [45] Patented Oct. 5, 1971 i [32] Priorities May 28, 1968 Primary Examiner-Lester M. Swingle [33] Austria Assistant Examiner-David R. Melton [31] 9 A 5093/68 37b; Attorney-Richard Low Aug. 16, 1968, Switzerland, No. 12 335/68 ABSTRACT: A hydraulic stressing press to be used for stressing at least one rod, wire or wire bundle which is prestressed in a concrete structure. The housing of the press is adapted to be supported against an abutment member and is provided with an anchoring device and a clamping device. The [54] FOR PRESTRESSING RODS IN anchoring device and the stressing device itself are actuated 21 Cl i 7 D in s by hydraulic pistons. An externally located anchoring ring 8 raw 8 lg cylinder unit is provided; and at least one part of this unit sur- [52] US. Cl 254/29 A rounds an internal clamping device and is connected to a [51] E2lb 19/00 anchoring element removably arranged between the clamping [50] Field of Search 254/29 A device and the clampingjaws.

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APPARATUS FOR PRESTRESSING RODS IN CONCRETE BACKGROUND OF THE INVENTION The invention relates to a hydraulic stressing press for stressing at least one rod, wire or wire bundle in prestressed concrete structures, having a press housing which is adapted to be supported against an abutment member and which is provided with an anchoring device having. anchoring jaws, for anchoring an end of said rod, wire or handle in prestressed condition on said abutment member, a clamping device having clamping jaws for gripping an end of said rod, wire or bundle and a stressing device for stressing said rod, wire or bundle by means of said clamping device, at least the anchoring device and the stressing device being actuated by hydraulic pistons arranged in cylinder chambers.

In a known stressing press of this type, a fluid conduit is taken forward to a position outside the press housing for the forwardly located anchoring cylinder. When the clamping jaws require changing, this conduit has to be removed, which involves a risk of the pressure fluid becoming contaminated. The overall length of the anchoring piston thus increases the length of rod required for engagement with the clamping jaws.

In an alternative stressing press the fluid supply is taken through a ring chamber between two external cylinder tubes of the press housing. This design is costly to produce and unnecessarily increases the weight of the presses. Both cylinder parts have to withstand high pressures, and their deformation must not impair the functioning of the apparatus. When changing the clamping jaws, two large annular sealing surfaces have to be exposed. This is very cumbersome and it is substantially never possible to perform this without contaminating the pressure fluid and without fluid loss. This may lead to operational breakdowns. Above all it is only possible to provide the anchoring piston with a small end face, so that it is necessary to operate with a quite high fluid pressure and close fits, which necessitates additional reinforcement of both cylinder tubes.

SUMMARY OF THE INVENTION It is an object of the invention to provide a stressing press which is as simple and light as possible, and yet is robust, compact and reliable in operation, avoiding the disadvantages described above, with facilities to allow the clamping jaws to be conveniently and quickly changed without contamination or loss of the pressure fluid.

This is achieved in accordance with the invention in that an externally located anchoring ring cylinder unit is provided, at least one part of which surrounds the internally disposed clamping device and is connected to an anchoring element removably arranged between the clamping device and the anchoring jaws. Arranging the anchoring piston at the rear of the clamping device with a e.g., tubular anchoring element which acts forward along the clamping device gives further structural advantages.

The anchoring piston surface in this embodiment is easily made large enough to allow operation at lower pressures. When the said piston is arranged at the forward end of the press, its cylinder forms an annular bead behind which an external fluid supply conduit may be attached without being subject to any substantial risk of damage. To give access to the clamping jaws, only the mechanical couplings are released, i.e., the hydraulic system remains completely unaffected. The distance between the clamp jaws and the anchoring clamps is substantially reduced, so that the necessary length of rod or wire to be inserted into the press is substantially reduced.

All parts located in front of the clamping device may be provided with wide tolerances which reduces the costs of manufacture, reduces the sensitivity to dirt and other external influences and increases the life. With the anchoring piston arranged as described, the operating fluid supply may be connected direct within the housing without exposed pipe lines or cumbersome supplies.

BRIEF DESCRIPTION OF DRAWINGS Reference should now be made to the accompanying drawings in which:

FIG. 1 is a longitudinal section through a stressing press of the invention;

FIG. 2 is a section through this press taken on the line Il-II of FIG. 1;

FIG. 3 is a partial plan view of the hose connection of the press of FIG. I;

FIG. 4 is a partial section through a modified embodiment of the invention;

FIG. 5 is a longitudinal section through a further embodiment of a press in accordance with the invention;

FIG. 6 is a fragmentary section through an alternative form of stressing press; and

FIG. 7 is a section through a further embodiment.

DESCRIPTION OF PREFERRED EMBODIMENTS In FIG. 1 the numeral 1 denotes an abutment surface of an abutment or a concrete member to be prestressed, from which there projects a steel rod, a wire or a bundle of wires 2 to be tensioned. The numeral 3 denotes an anchoring ring of an anchoring device generally denoted by V, which is provided with a bevelled surface 4 internally and receives three segment-shaped anchoring jaws 5. The jaws are wedge displaceable along the bevel surface 4 and are provided on their inside surface with sawtooth serrations 6 which, when pressure is exerted from the right in FIG. 1 against the jaws, dig into the rod 2 and retain it firmly, the jaws being self-locking on the surface 4.

The stressing press is thus formed of a supporting body 18 with supporting tube 9, and the clamping piston 15, which acts on the anchoring jaws 5 via pressure tube 16 and body I7. The piston 15 is guided in an intermediate cylindrical member 11 to which the stressing cylinder tube 13 in which the stressing piston 28 is slidably mounted, is fastened.

The press clamp K is connected via tension tube 270 to the stressing cylinder, and with the clamping tube 16 forms also the return piston. The clamp K comprises a housing 23 and the clamping jaws 21. The jaws in this case are hydraulically actuated by a piston 40 and a separate hydraulic pipeline.

The anchoring piston 15 and the return piston 27 thus have a common cylinder chamber 29. The latter communicates with a pressure supply hose 35, while the stressing cylinder chamber 30 communicates with a pressure supply hose 34. The oil supply 38 shown for the clamping piston 40 may optionally communicate with the fluid chamber 30 or it may receive a separate fluid pipe (from the rear).

During the stressing operation the whole eflective piston surface of the piston 28 is under pressure. Since during anchoring, when the pressure medium enters via the passage 35 into chamber 29 and the pipe 34 is shut off, the annular surface 290 of the return piston is acted on, the pressure in the sealed cylinder chamber 30 is increased. Since, however, the anchoring ring pressure surface 29b is relatively large, only a low anchoring pressure is required and it is therefore possible to control the pressure rise in the chamber 30 during the anchoring operation. The piston rod 27a is also subjected to a correspondingly increased force. Its external diameter should therefore be selected such that the eflective piston surface 29a of the return piston becomes small relative to the stressing piston surface.

As far as the connection of the piston 40 via the bore 38 with the cylinder chamber 30 is concerned the stressing piston surface 28 is made no larger than the two surfaces 290 and 29b. It is therefore possible to exert relatively large forces against the clamping jaws without exerting additional forces against the abutment surface, which would begin the stressing operation. To carry out a stressing operation, pressure fluid is first of all supplied via the hose 34 to the cylinder chambers 30 and 39, the conduit 35 of the chamber 29 being kept at a limited lower pressure by a pressure reduction valve, thus first closing the clamping jaws 21. The chamber 29 is then opened to exhaust and the pistons 28 and 27 together with the whole clamping device move to the right, the rod 2 to be stressed which is held at the opposite end, is stressed and the fluid pressure rises, which results in a progressively increasing clamping force. To release the rod the anchoring piston 15, which is subject to return pressure, may move to the right, or may be forced to the right by a spring (not shown), so that pressure against the anchoring jaws is omitted, and the stress rod 2 can be freely pulled longitudinally with respect to the anchoring aws.

When a predetermined stressing distance or a predetermined intermediate pressure has been attained, the pipe line 34 is first shut off and the pipe 35 leading to chamber 29 subjected to a low pressure. Thus the stressed rod is retained by the clamping jaws, now stationary, while the anchoring piston 15 via the parts 16 and 17 forces the jaws in, rigidly locking the stress rod 2 in the clamping ring.

If line 34 is drained, clamping jaws 21 are released and open with the following moving back of the press housing to right under the pressure acting on the return piston when abutting face 20 of anchoring ring 17.

To change the clamping jaws the union nut is first slackened and the supporting tube 9 drawn off. Then the clamping thrust member 16 may be lifted out, and the clamping ring 23 unscrewed by means of a spanner inserted in the bores 41. Since this occurs in the return end position, the surface of the piston rod 16 swept over by the seal of the return piston 47 is not impaired. Even the smallest particles of dirt are in this way kept away from the hydraulic fluid.

The embodiment shown in FIG. 4 differs from that described in that a helical compression spring 42 is inserted in the cylinder chamber 39 of the return piston 27', which spring acts on the clamping jaws 21'by means of a thrust washer 43. The anchoring thrust washer 17 is provided with stamped out annular stops l9 and which act on both of aws.

As shown in FIG. 5, a separate cylinder chamber 114 is provided for the clamping piston. This may be expedient for more accurately controlling the clamping, when the return piston is located at a different point of the stressing press, or when the return suction is obtained by alternative measures. The piston rod for anchoring in this case is shown acting externally, and may, for example, act on the piston 56 via the member 59 by means of studs 57 in a slot 58. I

Jaw change in this case is effected by removal of simple mechanical components.

The piston rod 127 is provided with a tubular extension 60 which projects through a cover 61 closing the stressing cylinder 113 at the rear and permeable to air, but substantially protecting it against contamination. The extension 60 may be provided with a marking or scale which indicates the amount of extension applied to a stressed rod. By means of a key 62 the extension engages in a suitable key groove of the cover 61 and thereby forms a safeguard against rotation of the clamping device.

According to the fragmentary view of FIG. 6, an anchoring cylinder 64 is formed at the front end of the supporting tube 9, the cylinder chamber 65 of which accommodates an anchoring piston 66 which is sealingly mounted inside against the supporting tube and the movement of which is limited by an annular flange 18' screwed into the cylinder. This flange forms a stop and guide for the anchoring plate 17 and engages the anchoring ring 3. The anchoring piston encloses the clamping ring 23' with radial clearance; the ring is screwed into the return piston 27'.

In this embodiment it is necessary for a connecting pipe for the anchoring cylinder to be drawn forwards, but this may be embedded in a recessed ring chamber and is protected forwardly by the cylinder itself; alternatively a longitudinal groove may be formed in the supporting tube 9 to receive the pipeline. In place of an outwardly open longitudinal groove a longitudinal rib may be provided in which a bore for the oil supply is formed.

In this embodiment the sealing effect between the parts 64 and 66 remains unaffected when the flanged ring 18' is screwed out. Though the whole supporting force has to be transmitted by the flanged ring to the cylinder 64, it is necessary only for the supporting ring to be lifted off to remove the ring 17 and to allow access to the clamping ring 23' so that it can be unscrewed.

As shown in FIG. 7 a stress piston 28 is connected by means of a tubular extension 67 to a piston base 68 which is mounted sealingly in the anchoring pressure pipe 16". The piston 15" may be biased by a return spring 69 or as shown in the lower portion a sealed air chamber 70 may be provided in the anchoring cylinder. The moving distance of the anchoring piston is 5 cm. longer than the distance needed for anchoring. The stressing rods may be stressed by this additional distance and then released, before the clamping means is caused to engage. This is desirable when the stress members are laid arcuately, to take into account the friction occurring thereby and make the stressing of these stress members or stress rods uniform. By this means it is possible to save between 10-1 5 percent of the stress rod cross-sectional area.

The pressure tube 16" engages a clamping thrust plate 17 which, like the piston base 68, is provided with apertures arranged symmetrically about the press axis for a group of stress rods 2. For each of these stress rods clamping jaws 21 biased by springs 70 are provided in the piston base, and in the anchoring thrust plate there are hollow pistons 71 which are urged by springs 72 to the left against their jaws 5 held together by a ring spring or a rubber ring. To retain the hollow pistons in the thrust plate 17" locking rings are used. The springs 72 cause a compensation of the pressure forces exerted on the anchoring jaws between the pressure plate and the plate 73.

This multiple stressing press is operated in the same manner as those described above. The thrust plate 17" may be freely removed to render the clamping jaws accessible by screwing the clamping rings 23" out. The pistons 71 may be formed as hydraulic pistons, the rings 72 being omitted, and if necessary commonly controlled hydraulic cylinders may be formed in the plate 17".

When the required stress length extension has been attained, the stress piston is run out further by a few cm., the anchoring jaws retained in engagement with the stress rods being carried along the excess stress distance. When the stress piston is moved back again, the anchoring jaws are again caused to engage with the anchoring plate 73 without their position relative to the stress rods having varied. The parts located towards the end of the stress rods, which due to the frictional forces might otherwise be excessively stressed in the central portion, may in this manner be relieved to such an extent that a substantially uniform tensional stress prevails over the entire length of the stress rods.

lclaim:

l. A hydraulic stressing press for stressing at least one rod, wire or wire bundle in prestressed concrete structures, comprising a press housing adapted to be supported against an abutment member said housing being provided with an anchoring device having anchoring jaws surrounding and anchoring an end of said rod, wire or bundle in prestressed condition on said abutment member, a clamping device having clamping jaws surrounding and gripping the end of said rod, wire or bundle outwardly of said anchoring device, a movable anchoring element interposed between the clamping device and said anchoring device engageable with said anchoring jaws and a stressing device engageable with said clamping jaws for stressing said rod, wire or bundle of said clamping device, at least the anchoring device and the stressing device being actuated by hydraulic pistons arranged in cylinder chambers, said cylinder chambers being located in an external anchoring ring cylinder at least one part of which surrounds the clamping device and has at its inner end an anchoring element arranged between the clamping device and the anchoring jaws.

2. A stressing press according to claim 2, wherein the anchoring piston is arranged behind the clamping device and said anchoring ring cylinder comprises a piston rod which is extended along the clamping device to the anchoring element.

3. A stressing press according to claim 2, wherein the piston rod is formed by an anchoring pressure tube concentrically enclosing the clamping device.

4. A stressing press according to claim 3, wherein the anchoring pressure tube is arranged within a housing supporting tube, which is secured to the rear housing part by means of a quick-release coupling.

5. A stressing press according to claim 1, wherein the effective piston surface of the anchoring piston is of such size that the required clamping force is obtained with a hydraulic pressure of less than 60 percent of the stressing pressure.

6. A stressing press according to claim 1, wherein said clamping device is provided with a housing fonned as a return cylinder and piston for said stressing device.

7. A stressing press according to claim 6 wherein the effective piston surfaces of the anchoring piston and of the return piston of the stressing device are aligned in the same direction in the same cylinder chamber.

8. A stressing press according to claim 6 including return and anchoring cylinders communicating with one another hydraulically wherein the effective piston surface of the return piston is smaller than the effective piston surface of the stress piston.

9. A stressing press according to claim 1, wherein the clamping device is provided with a separate actuating piston which has a passage for the rod to be stressed.

10. A stressing press according to claim 9, wherein when the clamping device is hydraulically actuated, the sum of the individual piston surfaces of the return piston and the anchoring piston being at least as large as the surface of the stressing piston.

11. A stressing press according to claim 1, wherein the piston of the stressing device has a tubular piston rod with a tubular rear extension which projects through a housing closure cover and engages the latter by means of a rotation preventing device.

12. A stressing press according to claim 9, wherein the cylinder chamber of the stress piston and the cylinder chamber of the clamping piston have separate fluid connections to which pressure fluid is applied separately.

13. A stressing press according to claim 1, wherein at least one piston rod of the anchoring device is exposed outside the housing member and engages through longitudinal slots of one housing part on the internally located anchoring element.

14. A stressing press according to claim 3, wherein the pressure tube is slidingly mounted on the supporting rod of the housing and the anchoring cylinder chamber is arranged outside the supporting tube.

15. A stressing press according to claim 1, wherein all control connections are mounted on a narrow partition ring member, on the two sides of which a tubular housing member and a stressing cylinder are secured by means of annular quick-release closure members.

16. A stressing press according to claim I, wherein in front of at least one part of the clamping device there is an opening stop for the clamping jaws.

17. A stressing press according to claim 1, comprising a return member for the anchoring piston, said member being a mechanical or pneumatic spring.

18. A stressing press according to claim 1, wherein the adjusting movement of the anchoring element is adapted to be larger than the moving distance of the anchoring jaws by an excess stressing distance of between 1 cm. and 5 cm.

19. A stressing press according to claim 1, wherein the clamping element and the base of a stressing piston are each provided with a group of apertures symmetrically arranged relative to the press axis to receive a group of stress rods, or bundles of stress rods, each of which apertures receives the individual stress rods or bundles of stress rods.

20. A stressing press according to claim 19, wherein each aperture of the anchoring element is provided with a hollow piston biased by an actuating member or compensation spring, which piston acts on the associated clamping jaws.

21. A hydraulic press for stressing a reinforcing member such as a rod, wire, or wire bundle in concrete structures comprising:

an elongated tubular housing surrounding said extending wire,

an anchoring device located exteriorly of one end of said housing adapted to abut against said concrete structure, said anchoring device including a plurality of jaws, engageable about said reinforcing member to secure the same in stressed condition,

a thrust body located within said housing and surrounding said reinforcing member adjacent said anchoring device, said thrust body being moveable into and out of engagement with said anchoring jaws,

a clamping device located within said housing including clamping jaws adapted to be secured about said reinforcing member outwardly of said anchoring device,

a piston surrounding said reinforcing member adjacent said clamping device and moveable into and out of engagement with said clamping jaws,

a stressing device comprising a piston,

piston rod means for selectively connecting said piston to said clamping jaws,

at least one tubular member located within said housing and defining therewith cylinder chambers associated with said thrust body, said clamping piston, and said stressing piston,

means for selectively delivering hydraulic fluid to said cylinder chambers to effect the sequential operation of said pistons to provide clamping stressing and anchoring of said reinforcing member,

said housing having an annular inwardly directed collar at one end for retaining said thrust body against axial movement and removable fastening means at its outer end to secure its tubular member therein. 

1. A hydraulic stressing press for stressing at least one rod, wire or wire bundle in prestressed concrete structures, comprising a press housing adapted to be supported against an abutment member said housing being provided with an anchoring device having anchoring jaws surrounding and anchoring an end of said rod, wire or bundle in prestressed condition on said abutment member, a clamping device having clamping jaws surrounding and gripping the end of said rod, wire or bundle outwardly of said anchoring device, a movable anchoring element interposed between the clamping device and said anchoring device engageable with said anchoring jaws and a stressing device engageable with said clamping jaws for stressing said rod, wire or bundle of said clamping device, at least the anchoring device and the stressing device being actuated by hydraulic pistons arranged in cylinder chambers, said cylinder chambers being located in an external anchoring ring cylinder at least one part of which surrounds the clamping device and has at its inner end an anchoring element arranged between the clamping device and the anchoring jaws.
 2. A stressing press according to claim 2, wherein the anchoring piston is arranged behind the clamping device and said anchoring ring cylinder comprises a piston rod which is extended along the clamping device to the anchoring element.
 3. A stressing press according to claim 2, wherein the piston rod is formed by an anchoring pressure tube concentrically enclosing the clamping device.
 4. A stressing press according to claim 3, wherein the anchoring pressure tube is arranged within a housing supporting tube, which is secured to the rear housing part by means of a quick-release coupling.
 5. A stressing press according to claim 1, wherein the effective piston surface of the anchoring piston is of such size that the required clamping force is obtained with a hydraulic pressure of less than 60 percent of the stressing pressure.
 6. A stressing press according to claim 1, wherein said clamping device is provided with a housing formed as a return cylinder and piston for said stressing device.
 7. A stressing press according to claim 6 wherein the effective piston surfaces of the anchoring piston and of the return piston of the stressing device are aligned in the same direction in the same cylinder chamber.
 8. A stressing press according to claim 6 including return and anchoring cylinders communicating with one another hydraulically wherein the effective piston surface of the return piston is smaller than the effective piston surface of the stress piston.
 9. A stressing press according to claim 1, wherein the clamping device is provided with a separate actuating piston which has a passage for the rod to be stressed.
 10. A stressing press according to claim 9, wherein when the clamping device is hydraulically actuated, the sum of the individual piston surfaces of the return piston and the anchoring piston being at least as large as the surface of the stressing piston.
 11. A stressing press according to claim 1, wherein the piston of the stressing device has a tubular piston rod with a tubular rear extension which projects through a housing closure cover and engages the latter by means of a rotation preventing device.
 12. A stressing press according to claim 9, wherein the cylinder chamber of the stress piston and the cylinder chamber of the clamping piston have separate fluid connections to which pressure fluid is applied separately.
 13. A stressing press according to claim 1, wherein at least one piston rod of the anchoring device is exposed outside the housing member and engages through longitudinal slots of one housing part on the inteRnally located anchoring element.
 14. A stressing press according to claim 3, wherein the pressure tube is slidingly mounted on the supporting rod of the housing and the anchoring cylinder chamber is arranged outside the supporting tube.
 15. A stressing press according to claim 1, wherein all control connections are mounted on a narrow partition ring member, on the two sides of which a tubular housing member and a stressing cylinder are secured by means of annular quick-release closure members.
 16. A stressing press according to claim 1, wherein in front of at least one part of the clamping device there is an opening stop for the clamping jaws.
 17. A stressing press according to claim 1, comprising a return member for the anchoring piston, said member being a mechanical or pneumatic spring.
 18. A stressing press according to claim 1, wherein the adjusting movement of the anchoring element is adapted to be larger than the moving distance of the anchoring jaws by an excess stressing distance of between 1 cm. and 5 cm.
 19. A stressing press according to claim 1, wherein the clamping element and the base of a stressing piston are each provided with a group of apertures symmetrically arranged relative to the press axis to receive a group of stress rods, or bundles of stress rods, each of which apertures receives the individual stress rods or bundles of stress rods.
 20. A stressing press according to claim 19, wherein each aperture of the anchoring element is provided with a hollow piston biased by an actuating member or compensation spring, which piston acts on the associated clamping jaws.
 21. A hydraulic press for stressing a reinforcing member such as a rod, wire, or wire bundle in concrete structures comprising: an elongated tubular housing surrounding said extending wire, an anchoring device located exteriorly of one end of said housing adapted to abut against said concrete structure, said anchoring device including a plurality of jaws, engageable about said reinforcing member to secure the same in stressed condition, a thrust body located within said housing and surrounding said reinforcing member adjacent said anchoring device, said thrust body being moveable into and out of engagement with said anchoring jaws, a clamping device located within said housing including clamping jaws adapted to be secured about said reinforcing member outwardly of said anchoring device, a piston surrounding said reinforcing member adjacent said clamping device and moveable into and out of engagement with said clamping jaws, a stressing device comprising a piston, piston rod means for selectively connecting said piston to said clamping jaws, at least one tubular member located within said housing and defining therewith cylinder chambers associated with said thrust body, said clamping piston, and said stressing piston, means for selectively delivering hydraulic fluid to said cylinder chambers to effect the sequential operation of said pistons to provide clamping stressing and anchoring of said reinforcing member, said housing having an annular inwardly directed collar at one end for retaining said thrust body against axial movement and removable fastening means at its outer end to secure its tubular member therein. 